The present invention relates to apparatus for extracting samples of liquid from flow lines or tanks.
Certain manufacturing operations require that the immediate or overall composition of a liquid flowing through a pipe or contained within a vessel or tank be monitored. Such monitoring ordinarily is accomplished with sampling apparatus, which takes samples of liquid from a main body of the liquid. Where a composite sample of the liquid is required, the sampler may be periodically operated to withdraw a series of small, measured amounts of the liquid as it passes a sampling point. The small, measured amounts are collected and admixed to form a representative sample of the total volume of liquid.
Other uses for samplers are in on-line analysis applications, in which the immediate composition of a liquid must be determined. For this application, the individual samples of liquid are not collected as a composite sample, but instead are received and analyzed separately.
Four exemplary types of sampling apparatus of the type contemplated by the prior art are disclosed in U.S. Pat. Nos. 4,147,062, 4,262,553, 4,475,410 and 4,744,255, issued to Ben E. Jaeger, the present inventor, and the teachings of all of which are incorporated herein by reference. Sampling apparatus of the type disclosed in said patents is attached to an access line to a pipe or vessel containing the body of liquid, so that a liquid sample receiving recess in a plunger of the sampler can be extended through the access line and an aperture in the pipe or vessel into the main body of liquid for receiving a liquid sample in the recess. The plunger is then retracted to deliver the liquid sample to a collection point in the sampler.
A disadvantage of the foregoing arrangement is that the sampler is always directly coupled through the access line with the body of liquid from which samples are to be taken, so that replacement, repair or maintenance of the sampling apparatus cannot be carried out without disturbing the body of liquid itself. This is because the sampler cannot simply be disconnected from the access line without causing uncontrolled escape of liquid from the main body through the access line. Consequently, before removal of the sampler, the main body of liquid must be interrupted, at least in the vicinity of the access line.
U.S. Pat. No. 4,628,732, issued Dec. 16, 1986 and the teachings of which are incorporated herein by reference, teaches a valve type connecting device for coupling a passive measuring instrument to a process having a parameter to be measured. The parameter may comprise temperature, density, pH value, consistency or some other characteristic of the process. The connecting device has a movable valve member through which a bore extends. The valve member is movable between positions placing the bore in and taking the bore out of communication with the process. The measuring instrument is connected to and received within the bore through the valve member. When the valve member is positioned to place the bore in communication with the process, the measuring instrument can be extended through the bore and into the process to measure a parameter of the process. To replace or repair the measuring instrument, the measuring instrument is retracted from the process and the valve member is moved to the position taking its bore out of communication with the process. The measuring instrument can then be disconnected from the valve member and removed from the bore without resulting in process escaping through and out of the bore.
While the apparatus of said U.S. Pat. No. 4,628,732 can couple a measuring instrument to a process having a parameter to be measured, the parameter must be of a type that is capable of being measured by an instrument that remains stationary in contact with the process, since the apparatus does not accommodate removal of a sampled portion of the process.